Spanish movie

I've turned into my father. This was me watching a foreign movie last night.
Me: This seems to be quite a bit of overreaction to seeing them have sex.
...
M: Wait a minute, who died?
B: The daughter.
M: What daughter?
B: The daughter.
M: She died? He killed her? Why would he have killed her?
B: The dog.
M: The dog?
B: Don't you remember how the dog was acting crazy and then she told it to guard the door, and then the girl came in?
M: ...Okay. Now the thing I don't understand is why the mother was babysitting her own daughter.
B: What?
M: That was the mother and the daughter... and the other one was also the daughter.
B: That's the babysitter and the babysitter has a mother but it is not the mother of the daughter.
M: Well why is the woman on the island so upset?
B: Because she's the mother.

It's like my brain has turned to sand.